This wait, also known as global cache buffer busy prior to Oracle 10g, specifies the time the remote instance locally spends accessing the requested data block. This wait event is very similar to the buffer busy waits wait event in a single-instance database.
High wait times on this event are often the result of:
Hot Blocks – multiple sessions may be requesting a block that is either not in buffer cache or is in an incompatible mode.
Inefficient Queries- as with the gc cr request wait event, the more blocks requested from the buffer cache the more likelihood of a session having to wait for other sessions.
Deleting some of the hot rows and re-inserting them back into the table may alleviate a Hot Block problem. Most of the time the rows will be placed into a different block and reduce contention on the block. The DBA may also need to adjust the pctfree and/or pctused parameters for the table to ensure the rows are placed into a different block.
Tuning queries to access fewer blocks in buffer cache will often result in less contention for the same block.